Factors influencing the variability of stable isotopes of carbon, nitrogen, and sulfur in benthic macrofauna from Admiralty Bay, maritime Antarctic

Abstract

This study examines benthic macrofauna from Admiralty Bay, maritime Antarctic, using triple stable isotope approach (δ¹³C, δ¹⁵N, and δ³⁴S) to assess the impact of melting glaciers and human activity on trophic interactions in this unique ecosystem. Four species – the limpet Nacella concinna, the sea urchin Sterechinus neumayeri, the starfish Odontaster validus, and the brittle star Ophionotus victoriae – were analyzed to characterize their isotopic composition and trophic niches. The results indicate that diet and feeding strategies were the main drivers of δ¹³C, δ¹⁵N, and δ³⁴S variability, demonstrating the utility of a multi-isotope approach for revealing diet composition, trophic plasticity, and benthic–pelagic coupling in polar benthic communities. Elevated δ¹³C values, typical of benthic primary producers, and depleted δ³⁴S values, indicative of sulfur derived from sediments, confirmed a strong reliance of benthic macrofauna on benthic food sources. In contrast, decrease in δ¹³C together with higher and typically marine δ³⁴S, can indicate higher contribution of pelagic diet sources. Spatial isotopic patterns further revealed areas influenced by glacial melt and shifting ice conditions, where consumers were relatively enriched in δ¹³C and δ¹⁵N compared to sites with rather open-ocean conditions. Notably, δ³⁴S emerged as a possible early indicator of human-related disturbance, with depletion reflecting increased anthropogenic sulfur inputs and reduced oxygen conditions in benthic habitats linked to nutrient enrichment. Concurrent to ³⁴S-depletion enrichment in ¹⁵N supports the role of nitrogen inputs from human activities. These findings demonstrate that stable isotopic tracers, particularly when incorporating sulfur alongside carbon and nitrogen, provide a powerful tool to detect and interpret ecological responses to both natural and anthropogenic drivers, offering insights into local ecosystem shifts and their broader implications for Antarctic food webs under climate change and growing human pressure.